Liquid crystal displays (LCDs) have advantages of portability, low power consumption, and low radiation. Therefore, LCDs are widely used in modern daily life. Typically, a color LCD displays images based on red (R), green (G), and blue (B) primary colors. In each of sub-pixel regions of the LCD, a respective one of the R, G, B colors is displayed. Each sub-pixel region can display the respective R, G, or B color in any one of a range of intensities called gray levels. Typically, there are 256 (8-bit) gray levels, which range from the 0th gray level to the 255th gray level. Each of the 8-bit gray levels corresponds to an 8-bit signal input to the LCD. An 8-bit data driver of the LCD receives the 8-bit signals for all the sub-pixel regions, and drives the LCD to display corresponding images. Thereby, the LCD can display images having as many as 16,777,216 (256×256×256) different colors.
However, due to cost issues, many or even most LCDs use a 6-bit data driver and a frame rate conversion (FRC) circuit. The 6-bit data driver and the FRC circuit cooperate to function as the equivalent of an 8-bit data driver. Referring to FIG. 3, this shows a conventional drive circuit 10 of an LCD. 8-bit input signals are converted into 6-bit signals by a frame rate conversion circuit 12. Each of the 6-bit signals represents one of 64 (6-bit) gray levels selected from the 8-bit gray levels. For example, the 6-bit gray levels may be the 0th, 4th, 8th, 12th, . . . , 248th, 252nd gray levels selected from the 8-bit gray levels corresponding to the 8-bit signals. A 6-bit data driver 14 receives the 6-bit signals, and drives the LCD to display corresponding images.
FIG. 4 is a diagram illustrating how the frame rate conversion circuit 12 operates. Each sub-pixel region of the LCD displays 6-bit gray levels in four successive frames so as to simulate an 8-bit gray level. For example, the four successive frames are a first frame, a second frame, a third frame, and a fourth frame. If the sub-pixel region displays the 4th gray level corresponding to a 6-bit signal in each of the first, second, and third frames, and displays the 8th gray level corresponding to a 6-bit signal in the fourth frame, the 5th gray level corresponding to an 8-bit signal is obtained as a visual effect. Similarly, if the sub-pixel region displays the 8th gray level corresponding to a 6-bit signal in the first and third frames, and displays the 4th gray level corresponding to a 6-bit signal in the second and fourth frames, the 6th gray level corresponding to an 8-bit signal is obtained as a visual effect. If the sub-pixel region displays the 4th gray level corresponding to a 6-bit signal in the first frame, and displays the 8th gray level corresponding to a 6-bit signal in the second, third, and fourth frames, the 7th gray level corresponding to an 8-bit signal is obtained as a visual effect. If the sub-pixel region displays the 4th gray level corresponding to a 6-bit signal in each of the four successive frames, the 4th gray level corresponding to an 8-bit signal is obtained as a visual effect. If the sub-pixel region displays the 8th gray level corresponding to a 6-bit signal in each of the four successive frames, the 8th gray level corresponding to an 8-bit signal is obtained as a visual effect. Thus, the 8-bit gray levels are obtained as a visual effect by displaying four successive 6-bit gray levels in a sub-pixel region.
However, if the 6-bit gray levels are periodically oscillated in a sub-pixel region, the LCD employing the frame rate conversion circuit 12 may have a side effect in that flickering may appear in the displayed images. When the LCD displays still images, the flickering is more obvious. As shown in FIG. 5, the frame rate of the LCD is 1/T. If the sub-pixel region displays the 4th gray level in four successive frames, and this happens repeatedly, the flickering rate of the LCD is 1/T. If the sub-pixel region displays the 8th gray level in four successive frames, and this happens repeatedly, the flickering rate of the LCD is also 1/T. If the sub-pixel region displays the 4th gray level in the first, second, and third frames and displays the 8th gray level in the fourth frame, and this happens repeatedly, the flickering rate of the LCD is 1/4T. If the sub-pixel region displays the 8th gray level in the first and third frames and displays the 4th gray level in the second and fourth frames, and this happens repeatedly, the flickering rate of the LCD is 1/2T. If the sub-pixel region displays the 4th gray level in the first frame and displays the 8th gray level in the second, third, and fourth frames, and this happens repeatedly, the flickering rate of the LCD is 1/4T.
The frame rate 1/T of the LCD is generally 60 hertz (Hz). Therefore, the flickering rate of the LCD may be 60 Hz, 30 Hz, or 15 Hz. If the flickering rate is 30 Hz or 15 Hz, the human eye can easily perceive the flickering of the images displayed by the LCD. In such cases, the display characteristics and performance of the LCD are reduced.
What is needed, therefore, is a liquid crystal display and a driving method for driving the liquid crystal display that can overcome the above-described deficiencies.